Could you share an example of your use case?
I have a hard time to imagine it’s movie night to wonder if I want to watch a 4:3, 16:9 or 21:9 movie… maybe I’m missing something that’s obvious to you 
As for adding information to movie posters…
let’s stick with the aspect ratio as that’s linked to your actual suggestion. There’s already a number of suggestions asking to include quality, language, content rating, user/audience/critic rating or original country… on top of the poster
e.g. Display Video Quality on Cover Art, Language Banners for Cover Art
